The invention relates to a device for processing a thin metal foil and provided with a frame plate with receiving and fixing means for a die, a guide plate with receiving and fixing means for a punch, and a guide arranging for the die and the punch to cooperate in the desired manner upon displacement of the frame plate and the guide plate towards each other for the purpose of processing a thin metal foil by the die and the punch.
With such devices used in practice, it has been found that due to tolerance, stiffness and guiding problems, it is not possible, by means of punching and transforming, to process foils having a thickness of less than 40 μm. This lower limit originates from an inventory which the inventor has made in the Dutch metal processing industry. The problems referred to are caused by the inaccuracy of the conventional devices as a result of:
1. The sum of the various tolerances upon assembly of the device from its various parts, as, typically, at the least the frame plate, the guide, the guide plate and the product-specific punch and die. These parts, and elements from which the parts, such as the guide, are assembled, are all, depending on the selected manufacturing technology, subject to tolerances, which may enhance each other upon assembly.
2. The stiffness of the assembled device may, in the case of static and dynamic forces and vibrations arising through process forces and movements during the processing operation, have its influence in that an inaccuracy in the relative position of punch and die may then arise.
3. The displacement of the punch relative to the die implies displacement of parts relative to each other, which is accompanied by respective play adversely affecting the accuracy of the device.
4. The device is overdetermined, so that a thermal expansion can occur in a variety of directions. The thermal center is undefined and thus the device is thermally unstable.
As a result of all these factors, among others, there is, as mentioned, a lower limit of 40 μm for working foils by means of punching and transforming, which precludes a number of applications of the processing technique. Thus, when punching thin sheet, a cutting gap (the distance between the punch and the die) is required which, as a rule, is from 3 to 10% of the sheet thickness. This means that for punching a sheet of 20 μm a cutting gap of from 0.6 to 2 μm is required, which is often less than the accuracy of the processing device. All this means that partly due to the static and dynamic inaccuracy of the known devices, working thin foils is not possible, which constitutes an impediment to the use of this technique in mass manufacture, which is precisely what this technique is eminently suitable for.